Phenolic foam

ABSTRACT

A phenolic foam having a density of from 10 kg/m 3  to 100 kg/m 3  and comprising a phenolic resin base part and a cellular part most of which is made up of a large number of fine cells, wherein the fine cells contain a hydrocarbon and have an average cell diameter of 5 μm to 200 μm, and the cell walls of at least most of the fine cells are formed of a smooth surface of the phenolic resin base. While the blowing agent is a hydrocarbon, the foam has a thermal conductivity comparable to that of a conventional foam made with a flon blowing agent, undergoes no change in thermal conductivity with time, exhibits excellent mechanical strength such as compressive strength, and has reduced brittleness.

TECHNICAL FIELD

This invention relates to a phenolic foam for heat insulation which isexcellent in heat insulating performance and mechanical strength and isenvironment-friendly.

BACKGROUND ART

Phenolic foam is useful as various constuctional materials because ofits superiority among resin foams particularly in flame retardance, heatresistance, low fuming properties, dimensional stability, solventresistance, and fabricability.

Phenolic foam is generally produced by expanding and curing a foamablecomposition prepared by uniformly mixing a resol resin obtained bypolymerization of phenol and formalin in the presence of under analkaline catalyst, a blowing agent, a surface active agent, a curingcatalyst, and other additives.

Blowing agents known for phenolic foam include so-called CFCs such astrichlorotrifluoroethane (CFC-113) and trichloromonofluoromethane(CFC-11), HCFCs such as dichlorotrifluoroethane (HCFC-123) anddichlorofluoroethane (HCFC-141b), HFCs such as 1,1,1,2-tetrafluoroethane(HFC-134a) and 1,1-difluoroethane (HFC-152a), and hydrocarbons such ascyclohexane, cyclopentane, and normal pentane (hereinafter referred toas HCs).

Among them CFCs have been used for preference for their advantages thatthey can be prepared with high safety, the gas they generate has a lowthermal conductivity, they exhibit excellent expanding properties inresol resins and easily form fine closed cells on expansion, and theresulting foams have a low thermal conductivity.

However, it recently turned out that CFCs and HCFCs decompose ozone inthe stratosphere to cause destruction of the ozonophere. Thesesubstances have now been recognized as a world issue as a cause ofglobal environmental destruction, and global restrictions have beenimposed on their production and use.

HFCs and HCs which do not destroy the ozonophere have then beenattracting attention as a blowing agent. Note is taken particularly ofuse of HCs as a blowing agent because of their smaller coefficient ofglobal warming than HFCs'.

HFCs and HCs are, however, difficult to apply as a blowing agent tophenolic foam on an industrial scale for such reasons as poor expandingperformance. In particular, application of an HC blowing agent has notyet succeeded in obtaining a phenolic foam with satisfactory heatinsulating performance on account of the high thermal conductivity ofthe blowing agent itself.

W097/08230 proposes a process of making a phenolic foam having a lowthermal conductivity by use of a hydrocarbon blowing agent, in which aresol resin containing substantially no free formaldehyde is used,stating that a phenolic foam having an initial thermal conductivity of0.0181 (kcal/m·hr·° C.) was obtained. Although the description statesthat the phenolic foam shows a small increase in thermal conductivity,the thermal conductivity of the phenolic foam shows a 10% or moreincrease up to 0.020 (kcal/m·hr·° C.) after 200 days. Further, thephenolic foam has fine holes in the cell walls as demonstrated inComparative Example 7 of the present invention. The large change ofthermal conductivity with time is assumed attributable to gradualdisplacement of the blowing agent with air through the fine holes of thecell walls.

JP-W-4-503829 (The term “JP-W” used herein means a “published Japanesenational stage of international application”) reports that addition of afluorocarbon to a hydrocarbon blowing agent leads to production of aphenolic foam with satisfactory heat insulating properties, givingExample in which a phenolic foam having a thermal conductivity of 0.0186W/m·K was obtained by using a pentane blowing agent to which aperfluorocarbon had been added. However, a phenolic foam prepared inaccordance with the description of the Example was found to have fineholes in the cell walls as revealed in Comparative Example 8 of thepresent invention. Addition of a perfluorocarbon, being expensive,creates another problem that the production cost will increase.

As stated above, we have had no phenolic foams which are produced byusing a hydrocarbon-containing blowing agent and yet exhibitsatisfactory heat insulating performance, excellent mechanical strength,such as compressive strength, and reduced brittleness.

An object of the present invention is to provide a phenolic foam whichhas a low thermal conductivity despite use of an HC as a blowing agent,undergoes little change in thermal conductivity with time, and hasexcellent mechanical strength, such as compressive strength, and reducedbrittleness.

DISCLOSURE OF THE INVENTION

The present inventors found that a resol resin whose reactivity fallswithin a specific range provides a phenolic foam having the cellularstructure as defined in the present invention when produced underspecific conditions of expansion and curing, the above object of theinvention can be achieved thereby. The present invention has beencompleted based on this finding.

The present invention provides:

(1) A phenolic foam having a density of 10 kg/m³ to 100 kg/m³ andcontaining a hydrocarbon, which is characterized by having an averagecell diameter in a range of from 5 μm to 200 μm, a void area ratio of 5%or less in its cross section, and substantially no holes in the cellwalls;

(2) The phenolic foam according to the above (1), which has a closedcell ratio of 80% or more, a thermal conductivity of 0.022 kcal/m·hr·°C. or less, and a brittleness of 30% or less;

(3) The phenolic foam according to the above (1) or (2), wherein thehydrocarbon is a constituent of a blowing agent;

(4) The phenolic foam according to the above (3), wherein the blowingagent comprises 50% by weight or more of the hydrocarbon;

(5) The phenolic foam according to the above (4), wherein the blowingagent contains 0.1 to 100 parts by weight of a fluorohydrocarbon per 100parts by weight of the hydrocarbon;

(6) The phenolic foam according to any one of the above (1) to (5),wherein the hydrocarbon is at least one compound selected fromisobutane, normal butane, cyclobutane, normal pentane, isopentane,cyclopentane, and neopentane;

(7) The phenolic foam according to any one of the above (1) to (6),wherein the hydrocarbon is a mixture of 5 to 95% by weight of a butaneselected from isobutane, normal butane and cyclobutane and 5 to 95% byweight of a pentane selected from normal pentane, isopentane,cyclopentane and neopentane;

(8) The phenolic foam according to the above (7), wherein thehydrocarbon is a mixture of 5 to 95% by weight of isobutane and 5 to 95%by weight of normal pentane and/or isopentane;

(9) The phenolic foam according to the above (5), wherein thefluorohydrocarbon is at least one compound selected from1,1,1,2-tetrafluoroethane, 1,1-difluoroethane and pentafluoroethane;

(10) A process for producing a phenolic foam, comprising mixing a resolresin having a viscosity increase rate constant of 0.005 to 0.5, a watercontent of 4 to 12% by weight and a viscosity of 1000 to 30000 cps at40° C., a surface active agent, a hydrocarbon-containing blowing agent,and a curing catalyst in a mixing machine having a temperature of 10 to70° C. and a pressure of from the vapor pressure of the blowing agent tothe blowing agent's vapor pressure plus 5 kg/cm², expanding the mixture,and elevating the temperature stepwise in a subsequent curing reactionstage;

(11) The process for producing a phenolic foam according to the above(10), wherein the hydrocarbon-containing blowing agent comprises 50% byweight or more of a hydrocarbon; and

(12) The process for producing a phenolic foam according to the above(11), wherein the blowing agent contains 0.1 to 100 parts by weight of afluorohydrocarbon per 100 parts by weight of the hydrocarbon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic illustrations of the cell wall structures ofphenolic foams, in which FIG. 1a is a schematic illustration of the cellwall structure according to the invention wherein the cell wall hassubstantially no holes; and FIG. 1b is a schematic illustration of thecell wall structure according to a conventional technique wherein thecell wall has holes or depressions.

FIG. 2 is an electron micrograph taken of the cell wall cut surface ofExample 1 which has no holes nor depressions.

FIG. 3 is an electron micrograph of the cell wall cut surface ofComparative Example 1 which has holes or depressions.

FIG. 4 is an electron micrograph of the cell wall cut surface ofComparative Example 7 which has holes or depressions.

FIG. 5 is an electron micrograph of the cell wall cut surface ofComparative Example 8 which has holes or depressions.

FIG. 6 is a photograph taken in Example 1 of a 100 mm by 150 mm area forvoid measurement.

FIG. 7 is a photograph taken in Comparative Example 1 of a 100 mm by 150mm area for void measurement.

In Figures numeral 1 indicates the surface of a cell wall; 2; a cellwall cut surface; and 3; a hole or a depression.

BEST MODE FOR CARRYING OUT THE INVENTION

The phenolic foam according to the present invention is one produced byusing a hydrocarbon-containing blowing agent. The hydrocarbon content inthe blowing agent is preferably 50% by weight or more, still preferably70% by weight or more, particularly preferably 90% by weight or more.With a hydrocarbon content less than 50% by weight, the blowing agentwill have an unfavorably increased coefficient of global warming.

The hydrocarbons which can be incorporated into the blowing agent usedfor production of the phenolic foam of the invention preferably includecyclic or acyclic alkanes, alkenes and alkynes having 3 to 7 carbonatoms. From the standpoint of expansion performance, chemical stability(having no double bond), their own thermal conductivity, and the like,alkanes or cycloalkanes having 4 to 6 carbon atoms are still preferred.Specific examples are normal butane, isobutane, cyclobutane, normalpentane, isopentane, cyclopentane, neopentane, normal hexane, isohexane,2,2-dimethylbutane, 2,3-dimethylbutane, and cyclohexane. Particularlypreferred of them are pentanes, i.e., normal pentane, isopentane,cyclopentane and neopentane; and butanes, i.e., normal butane, isobutaneand cyclobutane, because of their suitable expansion characteristics inthe production of the phenolic foam according to the invention and theirrelatively small thermal conductivity.

In the present invention these hydrocarbons can be used as a mixture oftwo or more thereof. For example, mixtures comprising 5 to 95% by weightof a pentane and 5 to 95% by weight of a butane are preferred for theirsatisfactory heat insulating properties over a broad temperature range.Mixtures comprising 25 to 75% by weight of a pentane and 25 to 75% byweight of a butane are still preferred. Inter alia, mixtures of normalpentane or isopentane and isobutane are preferred; because they secureexcellent heat insulating performance over a broad temperature rangefrom a low temperature region (e.g., heat insulators for freezers ofabout −80° C.) to a high temperature region (e.g., heat insulators forheating elements of about 200° C.) and also because the compounds arerelatively cheap, which is economically advantageous.

Where the hydrocarbon is used in combination with HFCs having a lowboiling point, such as 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane,and pentafluoroethane, as a blowing agent, the low temperaturecharacteristics of the phenolic foam can be improved. The HFCs can beused in an amount of from 0.1 to 100 parts by weight, preferably 5 to 90parts by weight, per 100 parts by weight of the hydrocarbon blowingagent. A mixed blowing agent comprising more than 100 parts by weight ofHFCs has an increased coefficient of global warming, which isunfavorable. The effect in improving low temperature characteristics issmall with a smaller HFC content than 0.1 part by weight.

For the purpose of controlling the foam initiating time, a low-boilingsubstance, such as nitrogen, air, helium or argon, can be added to theblowing agent as a foam nucleating agent in such an amount that does notimpair the cellular structure. A preferred amount of the foam nucleatingagent to be added is 0.05 to 5 mol %. If the amount of the foamnucleating agent exceeds 5 mol %, expansion tends to take placenon-uniformly, or the void tends to increase.

The phenolic foam according to the invention has a density of 10 kg/m³or more, preferably 15 kg/m³ or more, still preferably 20 kg/m ³ ormore, and 100 kg/m³ or less, preferably 70 kg/m³ or less, and stillpreferably 50 kg/m³ or less. If the density is less than 10 kg/m³, thefoam has reduced mechanical strength including compressive strength andis liable to break in handling due to increased brittleness, causingproblems on practical use. If the density exceeds 100 kg/m³, heattransfer in the resin part increases to reduce heat insulatingperformance.

The phenolic foam of the invention has a unique cellular structurehaving substantially no holes in the cell walls and comprising finecells of 5 μm to 200 μm in average cell diameter. Having virtually noholes in the cell walls, the phenolic foam of the invention contains thehydrocarbon used as a blowing agent in the production. The hydrocarboncontent in the phenolic foam of the invention is preferably 35% byweight or less, still preferably 20% by weight or less, and 0.05% byweight or more, still preferably 0.1% by weight or more. In general,foam is made up of fine spaces developed in a resin by vaporization of ablowing agent and a resin part existing among the spaces. In the presentinvention, the spaces are designated as cells, and the resin part as acell wall(s). The cells are usually about 5 μm to 1 mm in size.

The phenolic foam of the invention has an average cell diameter of 5 μmor greater, preferably 10 μm or greater, and 200 μm or smaller,preferably 150 μm or smaller. Because cell walls have limited thinness,a phenolic foam having an average cell diameter of smaller than 5 μm isof necessity to have an increased density. This means that the resinparts' contribution to heat transfer increases, which results ininsufficient heat insulation of the phenolic foam. If, on the otherhand, the average cell diameter exceeds 200 μm, radiant heat conductionincreases to lessen the heat insulating performance of the phenolicfoam.

Phenolic foams have relatively large spherical or amorphous vacancies(usually about 1 mm or greater in diameter; hereinafter referred to asvoids). It is considered that voids are generally formed due to joiningof cells, non-uniform vaporization of the blowing agent, or entrapmentof air, etc. in the stage of expansion. Voids not only cause reductionin compressive strength but impair the appearance. Voids are defined asfollows in the present invention. A phenolic foam is cut in parallel toits front and rear sides, and the vacancies present on the cut surfaceare measured by the method hereinafter described. Vacancies having anarea of 2 mm² or more are regarded as voids. The phenolic foam of theinvention has such few voids that the total void area is 5% or lessbased on the total area of the cut surface. Accordingly the phenolicfoam of the invention is characterized by small spread in compressivestrength. Further, there is produced an extremely excellent effect thatthe phenolic foam of the invention is easy to handle even in the form ofa thin foamed sheet of 10 mm or thinner which could be easily affectedby voids and has been difficult to handle in application. Furthermore,the phenolic foam of the invention is practically no inferior inappearance to insulators of other materials. A preferred void is 3% orless, particularly 1% or less.

The term “cell wall” as used herein means the phenolic resin partforming cells. In FIG. 1 are shown schematic illustrations of cell wallstructures. The phenolic foam of the invention has the cell wallstructure schematically shown in FIG. 1a. FIG. 1b schematically shows aconventionally produced phenolic foam obtained by using a hydrocarbonblowing agent. In FIG. 1b, a large number of holes or depressions(numeral 3 in FIG. 1) are observed on the cross section of the resinpart surrounded by three cells (hereinafter referred to as a cell wallcut surface (numeral 2 in FIG. 2)) and on the surface of internal cells(hereinafter referred to as cell wall surface (numeral 1 in FIG. 1)).The holes or depressions usually have a diameter of 50 to 1000 nm,frequently piercing the cell wall.

The phenolic foam according to the invention has substantially no holesnor depressions on the cell wall cut surface and the cell wall surfaceas shown in FIG. 1a. The language “substantially no holes nordepressions in the cell wall” means that the cell wall cut surface has10 or less, preferably 5 or less, holes or depressions per cell wall cutsurface under electron microscopic observation.

The mechanism of forming such holes or depressions is believed to bethat volatile components such as water separate and form lumps in aphenolic resin while the phenolic resin is curing and evaporate afterthe phenolic resin cures. It is said, in particular, that such holes ordepressions accelerate replacement of the blowing agent with air,resulting in an increase in thermal conductivity. The present inventorsconsider that the existence of the holes or depressions constitutes oneof main causes of the reduction in mechanical strength and the increasein brittleness of phenolic foams. The existence of the holes ordepressions is known, and attempts to eliminate them are seen, e.g., inJP-A-53-13669 and JP-B-63-20460, in which CFCs are used as a blowingagent. The techniques proposed consist in preparing a foamingcomposition having an increased viscosity by using a resol resin havingan extremely limited water content in JP-A-53-13669 or by using ahigh-molecular weight resol resin in JP-B-63-20460, thereby to improvethe cell wall strength and to eliminate holes or depressions of theresin part. According to the present inventors' researches, where an HCblowing agent is applied to these techniques, it is difficult to handlethe HC blowing agent and to raise the expansion ratio because of theincreased viscosity of the foaming composition. Phenolic foams preparedby using HCs as a blowing agent which have substantially no holes nordepressions and exhibit high performance has been unknown.

By allowing a resol resin having specific reactivity to expand and cureunder specific conditions, the phenolic foam structure of the presentinvention is obtained.

That is, in the present invention, a phenolic foam having a fine anduniform cellular structure with substantially no holes nor depressionsin the cell wall cut surface and the cell wall surface and with a smallvoid area can be obtained by preparing a foaming composition by mixingin a mixing machine under such conditions that expansion will haveproceeded to some extent when the composition is taken out of the mixingmachine, allowing the composition to expand further, transferring thecomposition to a curing reaction stage where the temperature is elevatedstepwise while releasing volatile components into a gas phase untilcuring completes.

The phenolic foam of the invention preferably has a closed cell ratio of80% or more, still preferably 85% or more, particularly preferably 90%or more. Where the closed cell ratio is less than 80%, the heatinsulating performance tends to be reduced considerably with timebecause the rate of replacing the blowing agent in the cells with airincreases. In addition, the foam will have increased brittleness,tending to fail to satisfy mechanical requirements for practice use.

The phenolic foam of the invention preferably has an initial thermalconductivity of 0.022 kcal/m·hr·° C. or less, still preferably 0.010kcal/m·hr·° C. to 0.020 kcal/m·hr·° C. The phenolic foam of theinvention also shows a reduced increase in thermal conductivity withtime, which is an important characteristic as a heat insulator. Thephenolic foam of the invention has an increase in thermal conductivityof 0.002 kcal/m·hr·° C. or less, preferably 0.001 kcal/m·hr·° C. orless, still preferably 0.0005 kcal/m·hr·° C. or less, after 300 days.Thus, the phenolic foam according to the present invention possessesexcellent heat insulating performance.

It is preferred for the phenolic foam of the invention to have abrittleness of 30% or less, particularly 1 to 20%. The phenolic foam ofthe invention thus exhibits marked improvement on brittleness.

The process of producing the phenolic foam of the invention will bedescribed.

The resol resin which can be used in the production of the phenolic foamis obtained by polymerizing phenol and formalin by heating at atemperature ranging from 40 to 100° C. in the presence of an alkalicatalyst. If desired, additives such as urea may be added in the resolresin polymerization system. Where urea is added to the resol resin, itis preferable that urea be previously methylolated with an alkalicatalyst. The methylolated urea is usually added in an amount of 1 to30% by weight of the resol resin. Because the resol resin as synthesizedgenerally contains excess water, the water content is adjusted to alevel adequate to expansion. In the present invention, the water contentis adjusted to 4% by weight or more, preferably 5% by weight or more,and 12% by weight or less, preferably 9% by weight or less. The resolresin to be expanded suitably has a viscosity of 1000 cps or more,preferably 3000 cps or more, and 30000 cps or less, preferably 2500 cpsor less, at 40° C. Where additives such as urea are added to the resolresin, it is required for the resol resin as containing the additives tohave the viscosity falling within the above-specified range.

In order to obtain the phenolic foam of the invention, curing reactivityof the starting resol resin (inclusive of the additives) is ofimportance. That is, the viscosity increase rate constant of the resolresin is 0.005 or more, preferably 0.01 or more, and 0.5 or less,preferably 0.35 or less, as obtained by the method hereinafter descried.If the viscosity increase rate constant is smaller than 0.005, thereactivity is so poor that the foaming composition is slow in raisingthe viscosity. It follows that the cell diameter becomes large,sometimes leading to foam breaks, and the foam performance is reduced.If the viscosity increase rate constant exceeds 0.5, the cell walls maybe bored, or the curing proceeds so fast that the viscosity increasestoo much during mixing in a mixing machine, etc. As a result, the mixingmachine tends to stop operating due to the elevated inner pressure or,in some cases, the resol resin may solidify completely in the mixingmachine to break the mixing machine.

The phenolic foam of the present invention can be obtained byintroducing a resol resin having moderate curability and having amoderately controlled viscosity, a blowing agent, a surface activeagent, and a curing catalyst into a mixing machine and uniformly mixingthem to obtain a foaming composition and allowing the foamingcomposition to expand and cure.

In general, the heat insulating performance and mechanical performanceof foam depend largely on the fine cellular structure. In other words,to have a high closed cell ratio and an average cell diameter rangingfrom 5 to 200 μm is significant. In order to form such fine cells, it isimportant that foam initiation takes place concurrently within a shorttime. Foaming initiates on vaporization of a blowing agent by the heatof reaction when a resol resin is mixed with the blowing agent and acuring catalyst or by the heat mechanically generated by the mixing.Then cells grow to form a cellular structure. The cellular structure isheavily influenced by the compatibility of the blowing agent, theprogress of vaporization of the blowing agent, the progress ofcrosslinking of the resol resin, and the like.

Control on the foam initiating point and the following cell growth isimportant for obtaining the cellular structure of the present invention.It is preferred that foaming initiates quickly after mixing the foamingcomposition and proceeds to some extent before the composition is takenout of the mixing machine. Such a state that a foaming composition hasstarted expansion when it is taken out of the mixing machine is known asa froth-foamed state. In order to obtain the foam of the invention, itis important to control this state of foaming under specific conditions.This state of foaming is controllable by the temperature and thepressure while the foaming composition is being mixed. It is generallysaid that the inner pressure of a mixing machine should be higher toprevent premature expansion. In the present invention, the pressure ofthe mixing machine is controlled within a proper range with the vaporpressure and the boiling point of the blowing agent used being takeninto consideration. Specifically, the pressure of the mixing machine isset at or above the vapor pressure of the blowing agent (or when theblowing agent is a mixture, the vapor pressure of the mixture) at thetemperature in the mixing machine and at or below (the vapor pressure +5kg/cm²). If the pressure in the mixing machine is lower than the vaporpressure of the blowing agent, expansion proceeds too much in the mixingmachine, and the cells gain in diameter to burst or join together intovoids. On the other hand, If the pressure exceeds (the vapor pressure ofthe blowing agent +5 kg/cm²), initiation of expansion or cell growthbecomes non-uniform. It follows that the cells have increased spread insize, or void formation may be induced, making it difficult to obtain asatisfactory foam. The pressure of the mixing machine is preferablycontrolled between (the vapor pressure of the blowing agent +0.5 kg/cm²)to (the vapor pressure of the blowing agent +3 kg/cm²). The temperaturein the mixing machine is 10° C. or higher, preferably 20° C. or higher,and 70° C. or lower, preferably 60° C. or lower. If the mixing machinetemperature exceeds 70° C., formation of many voids can result eventhrough the pressure falls within a proper range, or the pressure of themixing machine may elevate too high to operate.

In order to induce foam initiation in a short time, a low-boilingsubstance, such as nitrogen, helium, argon or air, may previously beadded to the blowing agent as a foam nucleating agent.

The curing reaction stage after expansion is also important forobtaining the foam of the invention. It is important to carry out curingreaction at a temperature increasing stepwise, i.e., the reaction isconducted in the initial stage at 70 to 90° C. for 1 minute to 1 hourand then at 90 to 100° C. for 10 minutes to 5 hours and, if desired, at100 to 130° C. for 10 minutes to 3 hours. The temperature differencebetween steps is 5° C. or more, preferably 10° C. or more.

The curing catalyst which can be used in expansion and curing includesaromatic sulfonic acids, such as toluenesulfonic acid, xylenesulfonicacid, benzenesulfonic acid, phenolsulfonic acid, styrenesulfonic acid,and naphthalenesulfonic acid, and a mixture of two or more thereof. Thecuring catalyst is usually used in an amount of 1 to 30 parts by weightper 100 parts by weight of the resol resin. Resorcinol, cresol,saligenin (o-methylolphenol), p-methylolphenol, etc. may be added as acure assistant. The cure assistant is usually added in an amount of 1 to300 parts by weight based on the curing catalyst. These curing catalystscan be used as diluted with a solvent, such as diethylene glycol orethylene glycol.

As a surface active agent for use in the present invention nonionicsurface active agents are effective. Included are alkylene oxides whichare ethylene oxide/propylene oxide copolymers, alkylene oxide/castor oilcondensates, alkylene oxide/alkyl phenol (e.g., nonyl phenol or dodecylphenol) condensates, fatty acid esters such as polyoxyethylene fattyacid esters, silicone compounds such as polydimethylsiloxane, andpolyalcohols. These surface active agents can be used eitherindividually or as a combination of two or more thereof. The surfaceactive agent is preferably used in an amount of 0.3 to 10 parts byweight per 100 parts by weight of the resol resin.

Methods of evaluating the tissue, the structure and the characteristicsof phenolic foams in the invention are then described.

The density as referred to in the invention is a value measured on asample, having a 20 cm-side square surface, of a phenolic foam fromwhich a facing material or a siding material, if any, has been removed.The weight and the apparent volume of the sample were measured, fromwhich the density was obtained according to JIS K7222.

The number of holes or depressions in cell walls as referred to in theinvention was measured as follows. A specimen of about 2 to 3 mm inthickness and about 1 cm² in area was cut with a trimming cutter out ofa cut surface of a foam, the cut surface being in approximately themiddle in the thickness direction of the foam and parallel with thefront and back sides of the foam. The specimen was fixed on a mount, andgold was sputtered thereon (15 mA, 3 mins). A micrograph was taken ofthe cell wall cut surface under a scanning electron microscope (HitachiS-800) at a magnification of 5000 times and observed. Ten cut surfaceswere observed, and the counts of holes or depressions were averaged formaking a judgement.

The void measurement in the present invention was made as follows. Aphenolic foam sample was cut in parallel with the front and back sidesin approximately the middle in the thickness direction. A 200% enlargedphotocopy was taken of an area of 100 mm by 150 mm of the cut surface(the length and the width were doubled to increase the area four-fold).The areas of voids each occupying eight or more 1 mm-side squares ofclear graph paper were added up to calculate the void area ratio. Beingan enlargement, the eight squares correspond to a 2 mm² area on theactual foam cut surface.

The closed cell ratio was determined as follows. A cylindrical specimenhaving a diameter of 35 to 36 mm was cut out of a phenolic foam by meansof a cork borer and trimmed to a height of 30 to 40 mm. The volume ofthe specimen was measured with a gravitometer of air comparison type(Model 1000, supplied by Tokyo Science) according to the standard usageas instructed. The difference between the specimen volume and the cellwall volume calculated from the specimen weight and the resin density isdivided by the apparent volume calculated from the outer dimensions ofthe specimen is taken as a closed cell ratio, which is in accordancewith ASTM D2856. The density of the phenolic resin was 1.27 g/cm³.

The average cell diameter of a phenolic foam as referred to in theinvention is a value obtained as follows. A foam was cut in parallel tothe front and back sides at approximately the middle in the thicknessdirection, and a 50-fold enlarged photograph was taken of the cutsurface. Four 9 cm-long straight lines were drawn on the photograph. Thenumber of cells on each line (the number of cells as measured inaccordance with JIS K6402) was counted, and an average of the counts wasobtained. A length of 1800 μm divided by that average cell number wastaken as an average cell diameter.

The compressive strength was measured in accordance with JIS K7220 on asample having a 50 mm-side square surface. A specified strain was set at0.05.

The thermal conductivity was measured on a specimen having a 200 mm-sidesquare surface in accordance with a plate heat flow meter method of JISA1412 between a 5° C. plate and a 35° C. plate.

The brittleness was measured as follows. Twelve 25±1.5 mm-side cubeswere cut out of a foam in such a manner that at least one face of eachcube is the molding skin surface or a facing material. Where a foam wasthinner than 25 mm, the thickness of the foam could be the thickness ofits specimen. Twenty-four 19±08 mm-side cubes of oak having been driedat room temperature and twelve test cubes were put in an oak-made boxhaving internal dimensions of 191×197×197 mm that could be closed tightso that dust might not come out. The box was revolved 600±3 times at aspeed of 60±2 rpm. After the revolution, the contents of the box weretransferred to a net having a nominal dimension of 9.5 mm and sieved toremove small pieces. The test pieces remaining on the net were weighed,and the weight reduction ratio calculated based on the weight of thetest cubes before testing was taken as a brittleness. The measurement isbased on JIS A9511.

The hydrocarbon or fluorohydrocarbon present in a phenolic foam wasmeasured as follows. A phenolic foam sample was put in a closed mixerand ground to destroy the cells. While being displaced with nitrogen,the gas phase was introduced into a gas absorbing tube containingpyridine. The hydrocarbon or fluorohydrocarbon dissolved in the pyridinewas analyzed by gas chromatography.

The viscosity increase rate constant, which is an indication of curingreactivity, was obtained by the following method.

To a resol resin weighing about 10 g was added a precisely weighed 5parts by weight, based on the resol resin, of a curing catalystcomprising 70 wt % of toluenesulfonic acid and 30 wt % of diethyleneglycol, and mixed well for 1 minute. The mixture was set in a rotationalviscometer (R100 Model Viscometer RE type, available from Tonen SangyoK.K.), and the viscosity at 40° C. was measured at a 30 second interval.The measurement results were plotted on a semilogarithmic coordinateswith the time as the X-axis and the logarithmic viscosity as the Y-axis.The plot from 4-minute to 10-minute was regarded as a straight line, theslope of which (1/min) was taken as a viscosity increase rate constant.

The viscosity of a resol resin was measured with a rotational viscometerat 40° C.

The water content of a resol resin was measured as follows. A resolresin was dissolved in dehydrated methanol (available from Kanto KagakuK.K.) whose water content had been measured in a concentration of 3 wt %to 7 wt %. The water content of the resulting solution was measured toobtain the water content of the resol resin. The measurement was madewith a Karl-Fischer moisture meter MKC-210 (available from Kyoto DenshiKogyo K.K.).

The present invention will now be illustrated in greater detail withreference to the following Examples and Comparative Examples.

The resol resins used in Examples and Comparative Examples were preparedas follows.

SYNTHESIS OF RESOL RESIN A:

In a reactor were charged 3800 g of 50 wt % formalin (available fromMitsubishi Gas Chemical Co., Inc.) and 3000 g of 99 wt % phenol(available from Wako Pure Chemical Industries, Ltd.) and agitated with apropeller agitator. The liquid temperature in the reactor was adjustedto 40° C. with a temperature controller. To the mixture was added 66 gof a 50 wt % aqueous solution of sodium hydroxide, and the temperatureof the reaction mixture was raised stepwise from 40° C. up to 85° C., atwhich the reaction mixture was maintained for 120 minutes. Then thereaction mixture was cooled to 5° C. The resultant reaction mixture wasdesignated resol resin A-1. Separately, 1080 g of 50 wt % formalin, 1000g of water, and 100 g of a 50% aqueous solution of sodium hydroxide wereadded to a reactor, and 1600 g of urea (guaranteed reagent, availablefrom Wako Pure Chemical) was added thereto, followed by agitation with apropeller agitator. The liquid temperature of the reactor was adjustedto 40° C. with a temperature controller. The temperature of the reactionmixture was raised stepwise from 40° C. up to 70° C., at which thereaction mixture was maintained for 60 minutes. The resulting reactionmixture was designated methylolurea U.

Resol resin A-1 (6800 g) was mixed with 1140 g of methylolurea U, andthe mixed liquid was heated to 60° C., at which it was maintained for 1hour and then cooled to 30° C. The reaction mixture was neutralized topH 6 with a 50 wt % aqueous solution of paratoluenesulfonic acidmonohydrate, and the reaction mixture was dehydrated at 60° C. Theresulting mixture was designated resol resin A.

SYNTHESIS OF RESOL RESIN B:

Resol resin A-1 was neutralized to pH 6 with a 50 wt % aqueous solutionof paratoluenesulfonic acid monohydrate, followed by dehydration at 60°C. The resulting reaction mixture was designated resol resin B.

SYNTHESIS OF RESOL RESIN C:

Resol resin C was synthesized in the same manner as for resol resin A,except that the weight of the 50 wt % formalin was changed to 3200 g andthat the weight of the methylolurea U to be added to 6000 g of the resolresin was changed to 770 g.

SYNTHESIS OF RESOL RESIN D:

Resol resin D was synthesized in the same manner as for resol resin A,except that the weight of the 50 wt % formalin was changed to 4200 g andthat the weight of the methylolurea U to be added to 5000 g of the resolresin was changed to 610 g.

SYNTHESIS OF RESOL RESIN E:

Resol resin E was synthesized in the same manner as for resol resin C,except that the resol resin was neutralized and dehydrated withoutadding methylolurea U.

SYNTHESIS OF RESOL RESIN F:

Resol resin F was synthesized as follows. In a reactor were charged 4360g of 50 wt % formalin and 3000 g of 99 wt % phenol and stirred with apropeller agitator. The liquid temperature in the reactor was adjustedto 40° C. by means of a temperature controller. To the reaction mixturewas added 66 g of a 50% aqueous solution of sodium hydroxide, followedby heating. When the solution viscosity at 25° C. fell to 62 cSt, thereaction mixture was cooled to 30° C. and neutralized to pH 6 with a 50wt % aqueous solution of paratoluenesulfonic acid monohydrate. Urea wasadded in an amount corresponding to 77 mol % based on the unreactedformaldehyde in the reaction mixture, and the reaction mixture wasdehydrated.

SYNTHESIS OF RESOL RESIN G:

Resol resin G was synthesized as follows. A 37 wt % aqueous solution offormaldehyde (3850 g) (guaranteed reagent, available from Wako PureChemical) and 3000 g of 99 wt % phenol were mixed, and 85 g of a sodiumhydroxide aqueous solution (10 N) was added thereto. The mixture washeated to 60° C. over 40 minutes, at which the mixture was kept for 30minutes. The temperature was further raised to 80° C., at which themixture was maintained for 30 minutes. The temperature was furtherelevated, and the mixture was refluxed for 40 minutes. Water was removedunder reduced pressure, and 727 g (corresponding to a concentration of13 wt % in the resol resin) of monoethylene glycol was added thereto toobtain resol resin G.

The water content, viscosity, and viscosity increase rate constant ofthe resol resins are shown in Table 1.

EXAMPLE 1

In resol resin A was dissolved 3.5 g, per 100 g of the resol resin, of asilicone type surface active agent (polyalkylsiloxane-polyoxyalkylenecopolymer, Paintad 32, available from Dow Corning Asia Ltd.). Theresulting resol resin mixture, a blowing agent (a mixture consisting of50 wt % of normal pentane (99+%, available from Wako Pure Chemical) and50 wt % of isobutane (purity: ≧99%, available from SK Sangyo K.K.) andhaving nitrogen dissolved therein in a concentration of 0.3 wt % basedon the blowing agent), and a curing catalyst (a mixture consisting of 50wt % of paratoluenesulfonic acid monohydrate (95+%, available from WakoPure Chemical) and 50 wt % of diethylene glycol (98+%, available fromWako Pure Chemical) were supplied to a pin mixer with a temperaturecontrolling jacket in a ratio of 100 parts by weight, 6 parts by weight,and 17 parts by weight, respectively. At this time the mixer temperaturewas 58° C., and the mixer pressure was 6.8 kg/cm² (absolute). Themixture coming from the mixer had started expanding, showing a so-calledfroth-foamed state. The froth was poured in a mold having nonwoven cloth(Spunbond E1040, available from Asahi Chemical Ind. Co., Ltd.) laidtherein. After the thickness was leveled, the upper surface was coveredwith the same nonwoven cloth, and the mold was closed. The mold wasdesigned so that water generated during curing might be released. Themold was kept in an oven at 70° C. for 30 minutes, in an oven at 90° C.for 1 hour and then in an oven at 100° C. for 1 hour. The results ofmeasurements made on the resulting phenolic foam are shown in Table 3.The electron micrograph taken for measurement of holes or depressions ata magnification of 5000 times is shown in FIG. 2. The photograph of acut surface for void measurement is shown in FIG. 6.

EXAMPLES 2 to 13 and COMPARATIVE EXAMPLE 1

The same procedure of Example 1 was followed, except for alterations tothe resol resin, the composition of the blowing agent, the mixertemperature, and the mixer pressure as shown in Table 2. The physicalproperties of the resulting foam are shown in Table 3. The electronmicrograph taken for holes or depressions measurement at a magnificationof 5000 times is shown in FIG. 3. The photograph of a cut surface forvoid measurement is shown in FIG. 7.

COMPARATIVE EXAMPLE 2

The same procedure of Example 1 was followed, except that alterationswere made to the resol resin, the composition of the blowing agent, themixer temperature, and the mixer pressure as shown in Table 2 and thatthe curing step was carried out at 80° C. for 5 hours. The physicalproperties of the resulting foam are shown in Table 3.

COMPARATIVE EXAMPLE 3

The same procedure of Example 1 was followed, except for using, as ablowing agent, a 1:1 by weight mixture of normal pentane havingdissolved therein 5 wt % of paraffin (first grade reagent available fromWako Pure Chemical; melting point: 44° C. to 46° C.) and 0.3 wt % ofnitrogen and isobutane, changing the mixer temperature and the mixerpressure to 74° C. and 8.5 kg/cm², and changing the curing conditions to80° C. and 5 hours. The physical properties of the resulting foam areshown in Table 3.

COMPARATIVE EXAMPLE 4

The same procedure of Example 1 was followed, except for using, as ablowing agent, a 1:1 by weight mixture of normal pentane havingdissolved therein 3 wt % of perfluoroether (Galden HT-70, available fromAusimont S.p.A.) and 0.3 wt % of nitrogen and isobutane, changing themixer temperature and the mixer pressure to 74° C. and 8.4 kg/cm², andchanging the curing conditions to 80° C. and 5 hours. The physicalproperties of the resulting foam are shown in Table 3.

COMPARATIVE EXAMPLE 5

The same procedure of Example 1 was followed, except for makingalterations to the resol resin and the mixer pressure as shown in Table2. The physical properties of the resulting foam are shown in Table 3.

COMPARATIVE EXAMPLE 6

The same procedure of Example 1 was followed, except for makingalterations to the resol resin and the mixer temperature and pressure asshown in Table 2 and changing the curing conditions to 110° C. and 3hours. The physical properties of the resulting foam are shown in Table3.

COMPARATIVE EXAMPLE 7

A weighed quantity (47.75 g) of resol resin F and a 1:1 by weightmixture of an alkyl phenol ethoxy ester (Harfoam PI, available fromHuntsman Chemical Co.) and an ethylene oxide-propylene oxide blockcopolymer (Pluronic F127, available from BASF) were mixed in a 2.25 gcup. With the mixture in the cup was further mixed 4.5 g of normalpentane at room temperature by stirring. To the mixture was furtheradded while stirring 5 g of a curing catalyst composition which was amixture of 35 g of resorcinol, 43.3 g of diethylene glycol, and 21.7 gof anhydrous toluene-xylenesulfonic acid (Ultra TX, available from WitcoChemical Co.). The contents of the cup was transferred into a mold whichhad previously been heated to 75° C. The mold was closed with a lid andput in an oven at 75° C. After 20 minutes, the foam was removed from themold and further cured at 70° C. for 3 hours. The electron micrographtaken at a magnification of 5000 times for holes and depressionsmeasurement is shown in FIG. 4. The physical properties of the resultingfoam are shown in Table 3.

COMPARATIVE EXAMPLE 8

To 100 parts by weight of resol resin G was added a previously preparedmixture consisting of 4.0 parts by weight of castor oil ethoxylate X (54mol of ethylene oxide per mole of castor oil) and 8.0 parts by weight ofcastor oil ethoxylate Y (54 mol of ethylene oxide per mole of castoroil). To the mixture was added a previously prepared mixture of 8.9parts by weight of normal pentane and 2.2 parts by weight ofperfluoropentane (PF-5050, available from 3M) at room temperature toform an emulsion. To the emulsion was added 17.5 parts of 50% sulfuricacid and mixed together. The mixture was poured into a mold, and themold was put in an oven at 60° C. for 1 hour to cure the foam. After 24hours from the preparation, the foam was cut to measure the physicalproperties. The electron micrograph taken for holes or depressionsmeasurement at a magnification of 5000 times is shown in FIG. 5. Thephysical properties of the resulting foam are shown in Table 3.

In Table 3, the mark “-” means “not measured”. In Comparative Examples 1to 6, since the compressive strength measurements showed spread due to ahigh void, the breadths of the spread are shown.

TABLE 1 40° C. Water Viscosity Resol Viscosity Content Increase RateResin (cP) (%) Constant (l/min) A 5100 6.2 0.08 B 3300 5.9 0.34 C 40006.4 0.04 D 5200 5.3 0.32 W 6000 8.5 0.65 F 5300 7.4 0.15 G 320 9.2 0.01

TABLE 2 Nitrogen Blowing Agent (wt % based Mixing Conditions Vapor onblowing Temp. Pressure*¹ Pressure*¹ Resin Compositional Ratio of BlowingAgent (%) agent) (° C.) (kg/cm²) (kg/cm²) Example 1 A n-pentane/50isobutane/50 — 0.3 58 6.8 5.5 Example 2 B n-pentane/50 isobutane/50 —0.3 53 6.2 4.9 Example 3 C isopentane/50 isobutane/50 — 0.3 46 5.5 4.3Example 4 D isopentane/50 isobutane/50 — 0.3 58 6.8 5.7 Example 5 Aisopentane/50 isobutane/50 — 0.3 54 6.6 5.2 Example 6 A isopentane/100 —— 0.3 57 4.1 2.5 Example 7 A n-pentane/100 — — 0.3 63 3.9 2.4 Example 8A n-pentane/50 n-butane/50 — 0.3 47 4.7 3.2 Example 9 A isopentane/50n-butane/50 — 0.3 51 4.6 3.8 Example 10 A isopentane/90 F-134a/10 — 0.355 5.0 3.3 Example 11 A n-pentane/60 F-134a/40 — 0.3 63 8.8 7.5 Example12 A isopentane/40 isobutane/40 F-134a/20 0.3 62 9.4 7.9 Example 13 An-pentane/40 n-butane/30 F-134a/30 0.3 61 8.9 7.2 Comp. Example 1 En-pentane/50 isobutane/50 — 0.3 61 7.1 5.9 Comp. Example 2 An-pentane/50 isobutane/50 — 0.3 73 8.3 7.7 Comp. Example 3 An-pentane/50 isobutane/50 — 0.3 74 8.5 7.9 Comp. Example 4 An-pentane/50 isobutane/50 — 0.3 74 8.4 7.9 Comp. Example 5 Dn-pentane/50 isobutane/50 — 0.3 58 15.0  5.5 Comp. Example 6 Bn-pentane/50 isobutane/50 — 0.3 54 6.1 5.0 Comp. Example 7 Fn-pentane/100 — — — *² *³ — Comp. Example 8 G n-pentane/80 perfluoro- —— *² *³ — pentane/20 *¹Absolute pressure; *²Standard temperature;*³Standard pressure

TABLE 3 Closed Average Cell HC Thermal Conductivity*² CompressiveBrittle- Holes Density Cell Ratio Diameter Content Immed. after 200 Dys.300 Dys. Strength ness or Void (kg/m³) (%) (μm) (wt %) Prepn. afterafter (kg/cm²) (%) Depressions*¹ (%) Example 1 28 96 102 4.3 0.01730.0176 0.0176 1.8 13 ∘ 0.5 Example 2 31 90 96 3.8 0.0179 — — 2.1 15 ∘0.4 Example 3 30 93 89 4.0 0.0177 0.0179 0.0180 1.9 10 ∘ 0.6 Example 429 92 97 4.1 0.0180 — — 1.8 13 ∘ 0.7 Example 5 29 92 93 4.1 0.0176 — —1.9 11 ∘ 0.5 Example 6 27 94 88 5.0 0.0175 0.0178 0.0178 1.7 8 ∘ 0.3Example 7 28 95 85 4.8 0.0182 — — 1.8 6 ∘ 0.4 Example 8 28 91 93 4.30.0180 — — 1.8 13 ∘ 0.5 Example 9 29 93 103 4.1 0.0176 — — 1.9 14 ∘ 1.1Example 10 30 91 112 4.1 0.0170 0.0173 0.0174 2.0 15 ∘ 1.3 Example 11 3089 121 3.0 0.0167 — — 1.9 13 ∘ 1.6 Example 12 29 90 108 3.6 0.0171 — —1.8 14 ∘ 1.1 Example 13 29 91 117 3.3 0.0169 — — 1.8 13 ∘ 2.0 Comp.Example 1 35 75 170 3.0 0.0223 0.0291 0.0298 0.9-1.9 38 x 8.8 Comp.Example 2 28 91 133 4.3 0.0195 — — 1.1-1.6 17 ∘ 6.4 Comp. Example 3 2992 124 4.0 0.0195 — 0.0217 1.0-1.5 15 ∘ 6.2 Comp. Example 4 29 90 1204.1 0.0190 — — 0.9-1.7 18 ∘ 6.5 Comp. Example 5 27 83 182 4.2 0.0205 — —0.7-1.4 34 Δ 6.5 Comp. Example 6 28 77 189 4.1 0.0225 0.0289 — 1.1-1.426 x 3.5 Comp. Example 7 24 88 230 5.6 0.0193 0.0214 0.0221 0.8 32 Δ —Comp. Example 8 38 85 260 3.7 0.0188 0.0219 — 1.6 37 x — *¹∘ = 10 orless; Δ = 11 to 50; x = 51 or more *²Thermal conductivity (kcal/m · hr ·° C.)

As demonstrated in the Examples, the phenolic foams according to thepresent invention, which are prepared by using a hydrocarbon blowingagent, exhibits such excellent heat insulating performance that thethermal conductivity is 0.022 kcal/m·hr·° C. or less and hardly changeswith time and have a so reduced void as can be handled stably even whenshaped into as thin plates as 10 mm or less.

To the contrary, although the phenolic foams shown in ComparativeExamples 2 to 4 have not more than 10 holes or depressions in the cellwall and exhibit excellent initial heat insulating performance, theyundergo changes in heat insulating performance with time. Further, ascompared with the present invention, they have such a high void that thecompressive strength tends to be low and shows large scatter and that athin sheet of 10 mm or thinner is liable to break.

The process shown in Comparative Examples 7 and 8 in which a liquidfoaming composition is expanded and cured has a larger expansion ratioto form cells of greater diameter when compared with the froth process.Besides, the cell walls suffer from holes or depressions, which isconsidered ascribed to non-uniform expansion.

INDUSTRIAL APPLICABILITY

The phenolic foam according to the present invention exhibits excellentheat insulating performance, excellent mechanical strength such ascompressive strength, and markedly reduced surface brittleness andtherefore is suitable as a constructional heat insulating material.Further, the phenolic foam of the invention is environment-friendlybecause the blowing agent used involves no fear of destroying theozonophere and has a small coefficient of global warming.

What is claimed is:
 1. A phenolic foam having a density of 10 kg/m³ to100 kg/m³ and containing a hydrocarbon, which is characterized by havingan average cell diameter in a range of from 5 μm to 200 μm, a void arearatio of 5% or less in its cross section, and substantially no holes inthe cell walls.
 2. The phenolic foam according to claim 1, which has aclosed cell ratio of 80% or more, a thermal conductivity of 0.022kcal/m·hr·° C. or less, and a brittleness of 30% or less.
 3. Thephenolic foam according to claim 1, wherein the hydrocarbon is aconstituent of a blowing agent.
 4. The phenolic foam according to claim2, wherein the hydrocarbon is a constituent of a blowing agent.
 5. Thephenolic foam according to claim 3, wherein the blowing agent comprises50% by weight or more of the hydrocarbon.
 6. The phenolic foam accordingto claim 4, wherein the blowing agent comprises 50% by weight or more ofthe hydrocarbon.
 7. The phenolic foam according to claim 5, wherein theblowing agent contains 0.1 to 100 parts by weight of a fluorohydrocarbonper 100 parts by weight of the hydrocarbon.
 8. The phenolic foamaccording to claim 6, wherein the blowing agent contains 0.1 to 100parts by weight of a fluorohydrocarbon per 100 parts by weight of thehydrocarbon.
 9. The phenolic foam according to any one of claims 1 to 3and 4 to 8, wherein the hydrocarbon is at least one compound selectedfrom isobutane, normal butane, cyclobutane, normal pentane, isopentane,cyclopentane, and neopentane.
 10. The phenolic foam according to any oneof claims 1 to 3 and 4 to 8, wherein the hydrocarbon is a mixture of 5to 95% by weight of a butane selected from isobutane, normal butane andcyclobutane and 5 to 95% by weight of a pentane selected from normalpentane, isopentane, cyclopentane and neopentane.
 11. The phenolic foamaccording to any one of claims 1 to 3 and 4 to 8, wherein thehydrocarbon is a mixture of 5 to 95% by weight of isobutane and 5 to 95%by weight of normal pentane and/or isopentane.
 12. The phenolic foamaccording to claim 7 or 8, wherein the fluorohydrocarbon is at least onecompound selected from 1,1,1,2-tetrafluorethane, 1,1-difluoroethane andpentafluoroethane.
 13. A process for producing the phenolic foam ofclaim 1 comprising mixing a resol resin having a viscosity increase rateconstant of 0.005 to 0.5, a water content of 4 to 12% by weight and aviscosity of 1000 to 30000 cps at 40° C., a surface active agent, ahydrocarbon-containing blowing agent, and a curing catalyst in a mixingmachine having a temperature of 10 to 70° C. and a pressure of from thevapor pressure of the blowing agent to the blowing agent's vaporpressure plus 5 kg/cm², expanding the mixture, and elevating thetemperature stepwise in a subsequent curing reaction stage.
 14. Theprocess for producing a phenolic foam according to claim 13, wherein thehydrocarbon-containing blowing agent comprises 50% by weight or more ofa hydrocarbon.
 15. The process for producing a phenolic foam accordingto claim 14, wherein the blowing agent contains 0.1 to 100 parts byweight of a fluorohydrocarbon per 100 parts by weight of thehydrocarbon.